1. Field of the Invention
The present invention relates to a camera system with interchangeable lenses, and more particularly such camera system including so-called electronic mount system for effecting communication of data required for various controls between a lens unit and a camera unit.
2. Related Background Art
The interchangeable lens system conventionally employed in ordinary still cameras is being introduced into so-called camcorders, with the recent progress in VTR and other imaging equipment. In employing such interchangeable lens system in the VTR or other similar equipment, the transmission of information can be conducted with an exposure state control signal that is so normalized and encoded as to sufficiently ensure the compatibility of lens control information, whereby the exposure control can be achieved, different from the conventional interchangeable lens system, in the same manner as in the fixed-lens camcorder.
FIG. 1 is a block diagram showing an example of the exposure control device in a conventional interchangeable-lens video camera system.
A chain line in the center indicates a mount portion MT, and a camera unit CM and a lens unit LS are respectively indicated at the right and at the left.
An object image formed on an imaging face of an image pickup device 3, through a lens optical system 1 and a diaphragm 2 is subjected to photoelectric conversion in the image pickup device 3 and is released as an image signal, which is supplied to a camera signal processing circuit 4. The circuit 4 effects for example .gamma.-conversion and obtains a color signal C and a luminance signal Y.gamma., which are converted into a composite image signal through a camera encoder 5 for example of NTSC format.
Also the luminance signal Y released from said camera signal processing circuit 4 prior to .gamma.-conversion is supplied to a detection circuit 6 and is for example integration detected for generating a control signal for controlling the diaphragm 2 in order to obtain an appropriate exposure according to the brightness of the object field.
The detection output signal from said detection circuit 6 is compared with a reference value 8 in a comparator 7, which thus calculates a difference signal. The difference signal is converted into digital data by an A/D converter 23, and is fetched in a microcomputer 20 of the camera side, then transmitted as a diaphragm control signal to a microcomputer 21 of the lens side, through a communication line 22 by predetermined communication means to be explained later.
In response, said microcomputer 21 in the lens unit LS calculates a signal representing the diaphragm control amount, which is converted into an analog signal by a D/A converter 24 and supplied to a diaphragm driver 9 for controlling the diaphragm 2.
FIG. 2 is a block diagram showing a manual exposure control device for an interchangeable-lens video camera system, wherein same components as those in FIG. 1 are represented by same numbers and will not be explained further. When an external input for effecting manual exposure control is given to the microcomputer 20 of the camera side, the status of such manual exposure control is transmitted to the microcomputer 21 of the lens side through the communication line 21.
In the lens unit LS in such a manual exposure control state, the value of a diaphragm encoder 11 is stored in a target value counter 12. The diaphragm control signal calculated by the lens microcomputer 21 is supplied to said target value counter 12 and added to the value of the diaphragm encoder stored therein. The sum obtained in the target value counter is compared with the value of the diaphragm encoder 11 by a comparator 13, and the driver 9 is activated according to result of said comparison, thereby controlling the diaphragm in such a manner that the value of the target value counter 12 becomes equal to that of the diaphragm encoder.
Thus, when an aperture opening switch 14 or an aperture closing switch 15 is actuated, the camera microcomputer 20 calculates the diaphragm control amount, which is transmitted through the communication line 22 to the lens microcomputer 21 and varies the value of the target value counter by a predetermined amount according to the actuation. The change in the value of the target value counter allows to vary the actual diaphragm aperture, through the operations explained above.
In such a device, however, when the lens is changed in the manual exposure control state, and if the target value counter of the newly mounted lens unit contains data at the previous use or erroneous data, it becomes impossible to control the diaphragm aperture to the target value prior to the lens change.